Described herein is a process for the fabrication of an electronic device. More specifically, described herein are catalyst compounds, and pre-mixtures, mixtures, and formulations comprising same, that are used for an alkoxysilane hydrolysis reaction in a semiconductor deposition process, such as without limitation, in a flowable chemical vapor deposition of silicon oxide.
Alkoxysilane compounds are useful as precursors for silicon-containing films (such as silicon oxide films) deposited by controlled hydrolysis and condensation reactions. Such films can be deposited onto a substrate, for example, by applying a mixture of water and alkoxysilanes, optionally with solvent and/or other additives such as surfactants and porogens, onto a substrate. Typical methods for the application of these mixtures include, without limitation, spin coating, dip coating, spray coating, screen printing, co-condensation, and ink jet printing. After application to the substrate and upon application of one or more energy sources such as, without limitation thermal, plasma, and/or other sources, the water within the mixture can react with the alkoxysilanes to hydrolyze the alkoxide and/or aryloxide groups and generate silanol species, which further condense with other hydrolyzed molecules and form an oligomeric or network structure.
Vapor deposition processes using water and a silicon containing vapor source for flowable dielectric deposition have been described, for instance, in U.S. Pat. Nos. 7,498,273; 7,074,690; 7,582,555; 7,888,233; and 7,915,131. Since the Si—C bond is relatively inert towards reaction with water, the resultant network may be beneficially functionalized with organic functional groups which impart desired chemical and physical properties to the resultant film. For example, the addition of carbon to the network may lower the dielectric constant of the resultant film.
Unfortunately, under certain deposition conditions, the hydrolysis and condensation reactions described above do not occur at a sufficiently fast rate to enable practical application of such precursors.
In processes where alkoxysilanes were synthesized, particularly when the synthesis was done by reacting a halosilane with an alcohol, crude complex mixtures that contain chlorosilane as an impurity in the desired product may form transiently. Such mixtures were never isolated nor made sufficiently pure under controlled conditions to be useful as an item of commerce.
The reference entitled “Alkoxysilated-Derivatives of Double-Four-Ring Silicate as Novel Building Blocks of Silica-Based Materials”, Hagiwara, Y. et. al., Chem. Mater. 2008, 20, pp. 1147-1153 (“Hagiwara”), teaches alkoxysilylated-derivates of siloxane cage compounds having a double-four-ring unit and their use as building blocks for xerogels or mesostructured films (Hagiwara at pg. 1148). For this purpose, the authors teach the synthesis and reactivity of dimethylethoxychlorosilane (Me2(EtO)SiCl), methyldiethoxychlorosilane (Me(EtO)2SiCl), and triethoxychlorosilane (Si(EtO)3SiCl), respectively (id.). Hagiwara further teaches that “[t]he reaction relies on the much higher reactivity of Si—Cl groups than the Si—OEt groups; therefore, the Si—Cl groups preferentially react with the Si—OH (or O—) groups of silicate species (id; citing the reference entitled “Formation of a New Crystalline Silicate Structure by Grafting Dialkoxysilyl Groups on Layered Octosilicate”, Mochizuki, D., et al., J. Am. Chem. Soc., 2002, 124, 12082-12083 (“As the silylating reagent, we used dialkoxydichlorosilane, (RO)2SiCl2, R=alkyl. Although both Si—OR and Si—Cl groups are reactive, the reaction rate of Si—Cl groups is much higher than that of Si—OR groups.”)). In Hagiwara, methyldiethoxychlorosilane ((Me(EtO)2SiCl) was synthesized by combining MeSiCl3 with ethanol. After removing species containing more than two Si—Cl groups under reduced pressure, the reaction mixture contained approximately 30% of the silylating agent MeSi(OEt)3 with the bulk of the material being Me(EtO)2SiCl as evidenced by NMR (id.).
GB Pat. No. 653238 (“GB '238”) teaches a process for interchanging the alkoxy and chlorine substituents of silanes to form silanes having both chlorine and alkoxy substituents on the same silicon atom. GB '238 teaches that the alkoxy chlorosilane reaction products may contain functionally inert monovalent alkyl or aryl radicals attached to the silicon atom through a carbon linkage in addition to the alkoxy and chlorine substituents (e.g., (CH3)2Si(OC2H5)Cl, C6H5CH3Si(OCH3)Cl, (C2H5)2Si(OC2H5)Cl, and CH3Si(OC2H5)2Cl) and silanes containing only alkoxy and chlorine substituents (e.g., (C2H5O)2SiCl2, (CH3O2)SiCl2, and (C2H5O)3SiCl) (see GB '238 on pg. 1, line 100 and pg. 2 lines 73-90). After separation of the reaction products, which is accomplished by fractional distillation, the alkoxy chlorosilanes may be condensed, without first being hydrolyzed, to form siloxanes (id.). Example 5 of GB '238 teaches the reaction of a mixture containing equimolar amounts of CH3Si(OC2H5) and CH3SiCl3 in the presence of HCl (which was contained in CH3SiCl3 as an impurity). After heating the mixture to 70° C., the mixture reacted to form CH3Si(OEt2)Cl2 and CH3SiCl2OEt, which was 96.7% of theoretical.
U.S. Pat. No. 4,228,092 (“U.S. '092”) teaches that the reaction of methyldichlorosilane (CH3SiCl2H) with methanol yielded a complex mixture of 92 percent methyldimethoxysilane with approximately 3 percent methylmethoxychlorosilane, approximately 4.7 percent methyltrimethoxysilane, and approximately 0.2 percent methyldimethoxychlorosilane (see U.S. '092 at col. 5, lines 57-67 through col. 6, lines 1-33). In example 3, U.S. '092 further teaches that reaction of ethanol with methyltrichlorosilane yields a crude mixture that is 97% methyltriethoxysilane and contains 1.8% methyldiethoxychlorosilane and 1% higher boiling point materials (id. at col. 8, lines 51-68 through col. 9, lines 1-4). This crude mixture was not isolated and was distilled to make substantively pure methyltriethoxysilane.
U.S. Pat. No. 7,629,227 (“U.S. '227) teaches a method for forming a flowable dielectric film that which involves a silicon-containing precursor and a catalyst selected from an ionizable species or a halosilane of formula R3SiX where R is independently selected from H, C1-C5 alkoxy and X is a halogen, amine or phosphine (see U.S. '227 at col. 6, lines 32-54). Examples of catalyst compounds include: (CH3O)3SiCl, (CH3CH2O)3SiCl, (CH3O)2Si(H)Cl, (CH3CH2O)2Si(H)Cl and (CH3)3SiN(H)Si(CH3)3 (id.). These Si-containing catalyst compounds may also provide at least some of the silicon that reacts to form the flowable film and/or be mixed with the silicon-containing precursor (id.). The U.S. '227 patent also teaches an embodiment wherein a trimethoxysilane ((CH3O)3SiH) precursor with a certain percentage of Cl impurity (in the form of (CH3O)2Si(H)Cl) is used (id.). The U.S. '227 patent further teaches that its silicon-containing catalyst compound is not limited to use with its analogous non-halogenated form but may also be used with another silicon-containing precursor (e.g., (CH3O)3SiCl may be the catalyst compound and TEOS the precursor) (id.).
Other chlorosilane species may also react with water rapidly to form hydrochloric acid in situ and could also serve as a catalyst for hydrolysis and condensation reactions. Unfortunately, alkoxychlorosilanes, alkoxysilanes and other similar compounds are known to undergo ligand exchange with each other, effectively scrambling the substituents on silicon. Under mild conditions, however, alkyl, aryl, substituted aryl, alkenyl and alkynyl substituents are largely immune to such scrambling.
Thus, there is still a need of a formulation comprising a silicon precursor and a suitable catalyst used for alkoxyalkylsilane hydrolysis reaction in semiconductor process such as flowable silicon oxide. In addition, there is a need of a formulation comprising a silicon-containing precursor and a catalyst compound that is selected to be mutually compatible with the silicon-containing precursor to provide a stable pre-mixture or formulation which can be stored, transported and delivered to an end user.